6. Upper Jurassic-Lowest Cretaceous Limestones Dredged from the Western Galicia Margin1

6. UPPER JURASSIC-LOWEST CRETACEOUS LIMESTONES DREDGED FROM THE WESTERN GALICIA MARGIN1 Pierre-Alain Dupeuble,2 Gilbert Boillot,3 and Denis Mougenot3 ABSTRACT Dredge samples of Upper Jurassic-lowest Cretaceous limestones were recovered from western Galicia margin. Lime• stones include benthic and/or planktonic assemblages, which were deposited in environments ranging from inner to outer shelf or upper slope. INTRODUCTION Clypeina jurassica Limestone The morphology of the western Galicia margin is controlled Clypeina is generally preserved in micritic limestone (PI. 1, by a complex network of Mesozoic and Cenozoic faults. Be• Fig. 1), though it also occurs in fine-grained pelloidal limestone cause of the thin sedimentary cover, fault scarps provide oppor• associated with other algae such as Taumatoporella parvovesi- tunities for sampling the basement rock and its overlying sedi• culifera (PI. 1, Fig.2). This facies indicates a shallow-water and ments (Upper Jurassic-lowest Cretaceous pre-rift sequence) by low-energy depositional environment. These limestones were prob• coring and dredging (Black et al., 1964; Funnel et al., 1969; Du• ably deposited during Kimmeridgian through Portlandian times peuble et al., 1976; Boillot et al., 1979; Mougenot et al., 1985). because Clypeina jurassica is not found in the Cretaceous of Al- These dredge and core samples supplement the drilling data from garve (south Portugal) (Ramalho, 1971; Durand-Delga and Rey, Deep Sea Drilling Project (DSDP) Site 398, which terminated in 1982). C. jurassica is, however, observed in the Portlandian- the Hauterivian syn-rift sediments (Sibuet, Ryan et al., 1979), Berriasian limestone of the western Pyrenees (Peybernes, 1976). and correspond to the limestone drilled at Site 639 during According to Bassoulet et al. (1978), this algae existed from the Ocean Drilling Program (ODP) Leg 103 (see Site 639 chapter, Kimmeridgian to the Berriasian, and culminated during late Kim• this volume). meridgian and Portlandian times. This paper focuses on the stratigraphy and paleoenvironment of the Upper Jurassic-lowest Cretaceous carbonates, which built Bacinella irregularis Limestone step scarps on the seafloor and were frequently sampled by dredg• Bacinella irregularis is preserved in many well-developed lime• ing on the Galicia, Vigo, Porto and Vasco da Gama Seamounts stone nodules and is commonly associated with Lithocodium (Fig. 1). The rest of the Mesozoic and Cenozoic rocks recovered aggregatum. Several authors (Bouroullec and Deloffre, 1968; in the dredges will not be discussed in this paper, as they were Ramalho, 1971) have emphasized the affinities between these poorly sampled and consist of Upper Cretaceous and Cenozoic two species, both of which encrust and, in some places, are the marl and shale with planktonic foraminiferal assemblages that dominant or only bioclastic component of the limestone. This were deposited in a deep-water environment (Boillot et al., 1979). sedimentary facies generally indicates a high- to moderate-en• Dredge samples contain limestone of Kimmeridgian through ergy depositional environment. However, Lithocodium aggrega• Berriasian age. Because of the dredging techniques, a single dredge tum appearing alone suggests a more protected environment. haul sometimes included samples from different stratigraphic The two algae are also associated in some samples with Cly• levels and/or paleoenvironments (Table 1). We, therefore, classi• peina jurassica (PI. 1, Fig. 3) or with less common Cayeuxia fied the carbonates recovered in the dredge according to their piae (PI. 1, Fig. 4). In those samples, an even more protected en• microfacies rather than according to stratigraphic succession. vironment seems to be indicated. According to Ramalho (1971), These carbonates can be divided into two main types: (1) lime• B. irregularis and L. aggregatum co-occurred during Portlan- stone containing a dominantly benthic assemblage, and (2) lime• dian-Berriasian time. stone having a dominantly planktonic assemblage. The latter type of limestone is rare. Oncolithic Limestone Oncolithic limestone is similar to that deposited in Algarve LIMESTONE WITH BENTHIC ASSEMBLAGES from Oxfordian to Portlandian time, mainly from the late Kim• Limestone having skeletal remains of a dominantly benthic meridgian to Portlandian (Ramalho, 1971; Durand-Delga and origin that were probably deposited in situ are termed limestone Rey, 1982), and is of Tethyan affinity. Many of the oncoliths are with benthic assemblages. built around a Nodophthalmidium clast, though they occur in some samples around a calpionellid lorica. Oncolithic limestones are generally deposited in moderate- to low-energy environments, probably on a more external part of the shelf than are the algae limestones described previously. Contribution No. 354 of the Groupe d'Etude de la Marge Continentale, Un• iversite Pierre et Marie Curie of Paris, and CNRS. Foraminiferal Limestone 2 Laboratoire de Geologie, Universite de Rouen, Faculte des Sciences, 76130 Mont-St.-Aignan (France). Most foraminiferal limestone samples recovered in the dredge 3 Laboratoire de Geodynamique Sous-Marine du CEROV, B.P. 48, 06230 Vil- are compositionally pelletoidal bioclastic wackestones to pack- lefranche-Sur-Mer (France). stones (PI. 2, Figs. 2 and 4), deposited in a low- to moderate-en- 99 P.-A. DUPEUBLE, G. BOILLOT, D.MOUGENOT Figure 1. Location of dredges (black arrows) where the Upper Jurassic-lowest Cretaceous carbonate platform was sampled. Locations of ODP Leg 103 Sites 637-641 and DSDP Site 398 are also shown (black dots). Bathymetric contours in meters. 100 JURASSIC-CRETACEOUS LIMESTONES Table 1. Classification of limestone samples recovered in dredge hauls. See Figure 1 for dredge locations. c -73 m "3 6 o Q 3 O Q o n vg | 3 rt c OS C a. u 06 Q S3 Pi <U oi 2 ro fi Q t» QCfl "> fi oo g a" oo g as o js a OH ° Limestone with Clypeina jurassica Limestone with Bacinella irregularis Oncolithic limestone Foraminiferal limestone Limestone with calpionellids ergy environment. In some samples, they resemble the sponge 1973; Jansa et al., 1980; Jansa, 1981). Their occurrence implies facies described on the Morocco margin by Steiger and Jansa an open sea and an active paleocirculation pattern between the (1984) (PI. 2, Fig. 3). Some of the foraminiferal limestones have Tethyan and Atlantic Oceans. The micritic limestone commonly a small amount of dolomite but lack a terrigenous component; associated with the calpionellids indicates a low-energy deposi- similar limestone was interpreted by Peybernes (1976) as having tional environment, possibly located on the upper slope, more been deposited in a very shallow-water environment. probably on the outer shelf. Many samples contain relatively common foraminifers char• acteristic of the Jurassic/Cretaceous boundary, such as Pseudo- CONCLUSIONS cyclammina lituus, Conicospirillina basiliensis, Trocholina elon- On the western Galicia margin, the oldest dated Mesozoic gata, T. alpina, and Nautiloculina oolitica. In addition, lime• sediments sampled by dredging are Tithonian limestones. The stones with Anchispirocyclina lusitanica were sampled southwest samples consist of platform carbonates, which are partly dolo- of Galicia Bank (Mougenot et al., 1985) near Site 639 (PI. 3, mitized and were deposited in a variety of paleoenvironments Figs. 1 and 2). According to Jansa et al. (1980) and to Durand- on a broad shelf. Micritic limestone with calpionellids were prob• Delga and Rey (1982), the top of the Anchispirocyclina layers ably deposited on an outer shelf or on the upper slope in an coincides with the upper limit of the Jurassic. In Algarve (Durand- open sea, which mixed easily with the Tethys and the central Delga and Rey, 1982), limestone with abundant Trocholina over• North Atlantic Ocean. In contrast, foraminiferal and algae lime• lies the Anchispirocyclina level. On the basis of facies similari• stones were probably deposited on the inner shelf. The lack of ties, we assigned a probable earliest Cretaceous age to samples detrital component suggests that the adjacent continent was flat having numerous Trocholina (PI. 2, Fig. 1). and protected from uplift and erosion, as expected during the pre-rift stage of the margin evolution. LIMESTONE WITH PLANKTONIC ASSEMBLAGES Limestone with planktonic assemblages was observed in only ACKNOWLEDGMENTS three samples: We thank M. Durand-Delga for help determining calpionellids and 1. A poorly cemented microbreccia dredged on the Vasco da M. Moullade, A. Meyer, and an anonymous reviewer for useful com• Gama Seamount (Fig. 1). The micritic clasts contain a calpio- ments on the first draft of this paper. nellid assemblage composed mainly of Calpionella alpina, Tin- tinopsella gr. carpathica, and Crassicolaria gr. intermedia (PI. 3, REFERENCES Fig. 3). The assemblage is late Tithonian in age. Bassoullet, J. P., Bernier, P., Conrad, M. A., Deloffre, R., and Jaffre• 2. A fine-grained limestone with micritic intraclasts sampled zo, M., 1978. Les Algues Dasycladales du Jurassique et du Cretace. on the Vigo Seamount. The assemblage consists of Calpionella Geobios Memoire, 2:330. Black, M., Hill, M., Laughton, A. S., and Matthews, D. H., 1964. alpina, rare Tintinopsella carpathica, and Crassicolaria parvu- Three non-magnetic seamounts off the Iberian coast. Geol. Soc. Lon• la. This assemblage was probably living during the Jurassic/ don, Q. J., 120:477-517. Cretaceous transition, possibly during the early Berriasian. Boillot, G., Dupeuble, P. A., Durand-Delga, M.,

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